In order to understand how the avian sarcoma virus (ASV) transforms normal mammalian cells to malignant ones, it is necessary to understand the molecular alterations that are induced by the transforming protein (pp60src) of the virus. The studies described in this research plan propose to identify and characterize cellular protein(s) which may be substrates of pp60src's kinase activity. This work will continue the investigation of the structure and role in cellular transformation of a P-tyr-containing 130,000 dalton protein that is immunoprecipitated by TBR serum from ASV-transformed vole cells. It will also complete the characterization of the 50K and 90K proteins complexed with pp60src in ASV-infected vole cells. Finally, this research will attempt to identify additional substrates of pp60src in these cells. The experimental techniques that will be employed to accomplish these objectives include: one- and two-dimension polyacrylamide gel electrophoresis, one- and two-dimension proteolytic peptide mapping, phosphoamino acid analysis, immunoprecipitation of antigens using antiserum against pp60src and the phosphotyrosine-containing tryptic peptide fragment of pp60src, biochemical subcellular fractionation, chromatin and chromatin-associated protein isolation and protein purification.